MANILA-- President Rodrigo Duterte vowed on Friday a full investigation into the killing of four soldiers by police officers in Jolo, Sulu, as he tried to ease tensions between the military and the police force.

Duterte visited soldiers in Zamboanga City to assure them of an impartial investigation into the incident that has marred ties between the military and the police.

"There is an investigation and I am giving you my word of honor that the investigation will proceed to find out the truth unfettered, unbridled by anybody," Duterte said in a speech.

" 'Yung totoo lang. 'Yun ang maasahan niyo. Kung sinuman ang may kasalanan, then he has to pay for it."

(Just the truth. You can count on that. Whoever is at fault has to pay for it.)

• NBI assesses statements of Sulu shooting incident witnesses

Friday's trip was Duterte's first speaking engagement in front of a crowd since the government imposed a lockdown in March.

The National Bureau of Investigation is studying the case that police initially labeled as a "misencounter."

Police alleged that the soldiers fled a checkpoint in Jolo on Monday and drew their guns at the officers, prompting them to fire.

Philippine Army chief Lt. Gen. Gilbert Gapay denied this, calling it “fabricated, parang sine (like in the movies).” He said the incident was a "rubout."

The soldiers, all intelligence operatives, were tracking two suspected suicide bombers from the terrorist Abu Sayyaf group when their van was flagged down by police at a checkpoint in Jolo.

Gapay said the soldiers cooperated and identified themselves as military personnel but they were still fired at.

Duterte recognized that the incident may have caused "animosity" between the Philippine National Police and the Armed Forces of the Philippines but urged both parties to "keep our silence" until the NBI releases the results of the investigation.

"Sinabi ko sa kaniya (NBI), imbestigahin mo. Search for the truth. Kung nakita na ninyo, make it public so that everybody will understand the situation," Duterte said.

The President said he wouldn't stop soldiers from retaliating, but said they should think of the consequences.

"Hindi ko kayo mapigilan. Kung gusto niyo gumanti, kung gusto niyo magresbak, go ahead, I will not stop you. But also at the end of the day, just give me one answer: Did the country benefit from furthering the violence?" he said.

(If you want revenge, go ahead. I will not stop you.)